1. Field of the Invention
The present invention relates to a system for improving the quality of water in the shallow water areas. More particularly, it relates to a method of and an apparatus for producing a circulatory water flow from the top toward the bottom and then from the bottom toward the top, to thereby increase the amount of oxygen that can be contained in the total water.
2. Description of the Prior Art
A conventional system has been used in those shallow water areas which are about two meters or less deep, and produces a circulatory flow of water over the water area from the top toward the bottom and then from the bottom toward the top. Specifically, the system includes a method and an apparatus described in the unexamined Japanese patent publication Nos. Showa 63-240989 and Heisei 2-50000.
In the conventional method and apparatus as mentioned above, a tubular construction which may be vertically installed in any shallow water area includes means for producing air bubbles at specific regular intervals. The air bubbles form an individual air bubble mass which rises through the tubular passage of the tubular construction due to its respective buoyant action while contacts with the whole inner wall of the tubular passage at the specific regular intervals. Under the buoyant action, the water above and below those respective air bubble masses can be drawn upwardly by the air bubble masses and will rise until finally the water is jetted out onto the surface from the top end of the tubular construction. Those jets of water ejected from the tubular construction diffuse radially over the water area. In this way, those portions of water which would normally stay near the bottom can be raised, and can produce a circulatory flow from the bottom toward the surface and then from the surface toward the bottom. Prior to the present invention, it has been known in the art that the technology as disclosed in the above respective publications provides the only effective means for improving the quality of water in shallow water areas in particular.
The method and apparatus described above are essentially provided for producing air bubbles at the particular regular intervals, and must therefore take into account physical dimensional requirements such as the relationships between the particular length and diameter of the tubular passages of the tubular construction for better performance when water is raised. In the shallow water areas (such as two meters or less deep), the length of the tubular construction is limited accordingly, and so the effective performance can only be achieved when a diameter of 20 cm or smaller is selected in relation to the length. In this case, it is difficult to raise a large amount of water at a time.
To avoid the above limitations, the conventional apparatus and method provide a solution whereby several smaller-diameter tubes, each of a given length, are bundled together to provide a greater diameter in total, or provide an alternative solution whereby any particular location where the installation is to be settled on the bottom is made deeper to allow for a longer passage and for the corresponding greater diameter passage. In either of these ways, more water can be raised. However, it should be noted that relying upon the buoyant action of the air bubbles restricts the flow rate of water being drawn by and raised with the produced air bubble masses. For example, the flow rate of the water that can be raised through the tubular passage is actually limited to 1.5 m/sec. As described, the amount of water to be raised at a time is limited by the small diameter of the tubular passage. This limitation may be removed by increasing the flow rate at which the water that can be raised. However, this is impossible according to the conventional method and apparatus, because the flow rate cannot be further increased. The amount of water to be raised can only be increased by increasing the number of tubular passages that are bundled together and installed in the shallow water areas.